Traditional analog and Time Division Multiplexed (TDM) telephone networks provide a “virtual direct connection” between endpoints with minimal perceived echo problems due to a pseudoacoustic effect of echo in a low delay environment. As telephone service providers deploy voice services using an Internet Protocol (IP) network and other packet switched networks, voice users, in particular, find some calls unacceptable as the additional packet delay causes echoes to have an increased perception. Much work has been done in the area of echo cancellation and improving voice quality for digital voice signals. Indeed, most gateway (GW) products now include echo cancellation as a network feature. The IP network that provides voice services are referred to as Voice-over-IP (VoIP) networks. Almost all VoIP networks also provide data services that are referred to as Voice Band Data (VBD) services. During a VBD call connection, any echo canceller in the communications path degrades the VBD service due to the echo cancellers' altering the data signal and causing unexpected errors.
According to International Telecommunications Union (ITU) standards, if a 2100 Hz tone is detected by any telecommunications switch, it disables its echo canceller. This is the reason that most modems send out a 2100 Hz Answer Back Tone (ABT) prior to any training and connection. However, there are still many modems that do not send out a 2100 Hz tone to disable echo cancellers in the communications path. These modems are widely used in Point of Service (POS) devices, such as credit card clients, that use a low rate modulation modem using v.32 and lower rate modulations, such as v.22, v.22 bis, etc. POS devices are sometimes alternatively referred to as point of sale devices.
Therefore, if an echo canceller is enabled during a VBD call, the connection is unreliable. If the echo canceller is disabled in the communications path (e.g., a voice gateway), during a voice call, it causes a normal voice call to experience an echo problem. Furthermore, if there is an echo canceller in the communications path external from a local gateway, there is no way to disable the external echo canceller for VBD calls through use of the local gateway.